Go to the Dashboard on your PC; click the Log heading.
Then under Food; there is the Food Plan which might say something like "Today I can eat 1367 cals".
You want to click the right arrow twice, till you see a screen with your desired weight, plan intensity and daily calorie deficit.
Click the Edit Plan button; enter current and goal weight then click Next.
You can pick a plan intensity which will set a calorie goal, or you can click link below "Set my own calorie target".
Then enter your target calories.
That's it; agree it's a bit hard to find eh.